The invention is useful in a piping system for distribution of high purity water to stabilize the purity of water or other fluid at or above a predetermined level. High purity water is only one fluid with which the invention may be used. It may also find utility maintaining a desired level of purity of other fluids in a piping system.
It has long been recognized that high purity water, which has less than one (1) part per million contamination as total matter and a bacteria count of less than one (1) colony per milliliter, is useful in performing certain test procedures in the medical arts and in research in other fields. By comparison, ultra-pure water is recognized as having less than one tenth (0.1) part per million contamination as total matter and less than one colony of bacteria per 100 milliliters. It has also been recognized that contamination occurs rapidly when the fluid remains static in the piping system. It is therefore standard practice in high purity water distribution systems to have a reservoir of water with the desired minimum solids content and which is chlorinated to destroy bacteria and to pump water from the reservoir to a distribution loop of the high purity water system. The main loop is connected to a plurality of individually controlled outlets and the water is constantly circulated through the distribution loop to be available at each outlet when needed. A treatment unit is included within the distribution loop through which the water is constantly circulated to keep the water in the main loop at the desired level of purity. The repurified water flowing through the distribution loop at all times is not as subject to contamination as is static water.
As is well known in the prior art, the material from which the piping is formed plays an important part in maintaining the water at a desired level of purity. Glass tubing has been found less than ideal because of the soluble inorganic materials present to some degree in all glass. Metal piping also gives off an undesirable amount of soluble inorganic solids. Plastic tubing offers the best material for delivering high purity water from a source of supply to the distant outlet. Teflon has been recognized as one of the most satisfactory plastics but because of its cost is used only in cases where other materials are not satisfactory for the desired purity of the water. Polyethylene and polypropylene tubing has been found satisfactory for the average high purity water system.
Even with the proper plastic material for piping and even with water being constantly pumped around the distribution loop and through the treatment unit, there remains a continuing source of contamination in the high purity piping systems of the prior art. That is found in the branch lines which extend between the distribution loop and the individual outlets spaced around the loop. Bacteria develop in the static water in branch lines whose outlets are not used for an hour or more. The bacteria inhabit the tiny recesses and openings in the walls of the tubing and in the connections which join the tubing together. The bacteria multiply in the static water in the branch line and migrate into the distribution loop and contaminate the water in the distribution loop before it is drawn from a downstream outlet. The prior art provides for effective disinfection of the water at the treatment unit in the distribution loop, but that often occurs only after the contaminated water has been innocently used at an outlet between a static branch line and the treatment unit, which might destroy the usefulness of an important project.
According to the prior art the branch lines and their outlets were purged manually by the users of the water with long purge times often resulting in an inadequate quality of purity. Timely manual purging is impractical and unreliable. The use of a continuous purge of these branch distribution lines and their outlets has been determined to be impractical due to increased pumping/energy cost especially where numerous outlets are employed. The routing of the main recirculating distribution loop by each outlet is not practical because of the increased length of the piping in the recirculating loop, which results in increased piping cost and consequently higher discharge pressures at the recirculating pump for maintenance of adequate fluid velocity. Yet, static pipe recontamination inevitably occurs without timely and systematic purging of the branch lines and their outlets.